The present invention generally relates to imaging with an Electron Beam Tomography (EBT) scanner. In particular, the present invention relates to measuring local lung function using an EBT scanner.
Medical diagnostic imaging systems encompass a variety of imaging modalities, such as x-ray systems, computerized tomography (CT) systems, ultrasound systems, electron beam tomography (EBT) systems, magnetic resonance (MR) systems, and the like. Medical diagnostic imaging systems generate images of a subject, such as a patient, for example, through exposure to an energy source, such as x-rays passing through a patient. The generated images may be used for many purposes. For instance, internal defects in a subject may be detected. Additionally, changes in internal structure or alignment may be determined. Fluid flow within a subject may also be represented. Furthermore, the image may show the presence or absence of components in a subject. The information gained from medical diagnostic imaging has applications in many fields, including medicine and manufacturing.
EBT scanners are generally described in U.S. Pat. No. 4,352,021 to Boyd, et al. (Sep. 28, 1982), and U.S. Pat. No. 4,521,900 (Jun. 4, 1985), U.S. Pat. No. 4,521,901 (Jun. 4, 1985), U.S. Pat. No. 4,625,150 (Nov. 25, 1986), U.S. Pat. No. 4,644,168 (Feb. 17, 1987), U.S. Pat. No. 5,193,105 (Mar. 9, 1993), U.S. Pat. No. 5,289,519 (Feb. 22, 1994), U.S. Pat. No. 5,719,914 (Feb. 17, 1998) and U.S. Pat. No. 6,208,711 all to Rand, et al., and U.S. Pat. No. 5,406,479 to Harman (Apr. 11, 1995). The above listed patents are referred to and incorporated herein by reference in their entireties.
As described in the above-referenced patents, an electron beam is produced by an electron source at the upstream end of an evacuated, generally conical shaped housing chamber. A large negative potential (e.g. −130 kV or −140 kV) on a cathode of the electron source accelerates the electron beam downstream along an axis of the housing chamber. Further downstream, a beam optical system that includes solenoid, quadrupole, and deflection coils focus and deflect the beam to scan along an x-ray producing target. EBT systems utilize a high-energy beam of electrons to strike the target and produce x-rays for irradiating an object to be imaged. The point where the electrons strike the target is called the “beam spot”. The final beam spot at the target is shaped as an ellipse and must be suitably sharp and free of aberrations so as not to degrade definition in the image rendered by the scanner.
The x-rays produced by the target penetrate a patient or other object and are detected by an array of detectors. The detector array, like the target, is coaxial with and defines a plane orthogonal to the scanner axis of symmetry. The output from the detector array is digitized, stored, and computer processed to produce a reconstructed x-ray image of a slice of the object, typically an image of a patient's anatomy such as the heart or lungs.
An EBT scanner allows for the collection of many angles of view and scanning of a number of slices in a short time. There is no mechanically moving gantry. Both high resolution and dynamic scanning modes may be provided while eliminating the need for any target or detector motion by replacing conventional x-ray tubes with electron beam technology.
Multiple views may be generated by magnetically steering a focused electron beam along a 210-degree target ring positioned beneath a subject. Opposite the target ring is a stationary detector ring of cadmium tungstate crystals encompassing a 216-degree arc above the subject. Photodiodes in the detector ring are used for recording transmitted x-ray intensity. X-ray intensity data may be processed to produce an image.
One important function of medical diagnostic imaging is measurement of lung function and lung capacity. Lung measurements may be used to diagnose diseases and other problems associated with a patient's lungs or lung function. Lung information may be used to diagnose and treat such conditions as emphysema.
Typically, a spirometer or other device that measures air flow rate is used to obtain lung function measurements. A patient takes a deep breath in and rapidly expels the air or exhales. The spirometer measures a change in air volume in the lung over time. Unfortunately, using a spirometer in this manner measures function only for the entire lung. Additionally, measurement using a spirometer is a coarse measurement and does not allow detection of fine changes in lung function, such as early onset of disease. Thus, a system allowing early detection of disease in the lung would be highly desirable. Furthermore, a system that allows measurement of a portion of a lung, rather than the entire lung, would also be highly desirable.
A spirometer measures lung function while a patient inhales and then exhales rapidly, typically over a period of 1-2 seconds. That is, a spirometer measures a volume of air that a patient inhales or exhales as a function of time. A spirometer may also measure a flow or rate at which the volume is changing as a function of time. Measurements are currently obtained for an entire lung. However, no good imaging method currently exists to scan this rapid change in lung volume along with the spirometer. Conventional CT imaging systems are not fast enough to take images of local lung function. Prior art systems attempted to obtain EBT images every 500 ms with a 100 ms scan time. Since the length of a lung inhalation-exhalation maneuver is only approximately two seconds, use of 500 ms results in sampling of a patient's lungs that is too coarse (low level of detail) to diagnose developing disease or other condition in the lung. Alternatively, the prior art employs a scan every 116 ms, which results in excessive radiation exposure dosage, particularly for children, teenagers, and young adults. Thus, a system that may scan quickly enough to obtain images of local lung function would be highly desirable.